Hello, I have an old 15 inch PowerBook and I've upgraded to the MBP just a few months ago. Until now I have come to buy an external hard drive to back it up. I was going to use the same one to transfer all of my music from the PB to the Pro, but it won't turn on! I had it shut down and unplugged ever since I got my Pro and haven't touched it since. Now when I get to wanting to transfer my music, all I get is a dark screen with a low beeping sound. I believe it's a HD failure since this is the second time it has done this. But from the last time, I don't remember a beeping sound, and it made it to at least a grey screen. This one won't even. I've had it plugged in for about 20 minutes and still nothing. The light on the lock button stays on, then blinks twice and stays on again.

I would think the screen should light up and give you a question mark if the hard drive failed. The dark screen and low beeping sounds like a logic board problem or maybe the power supply. Also, I don't know what the symptoms would be on a Powerbook if the PRAM battery died but on some PC notebooks when the CMOS battery dies, they do exactly what you described.